Susceptor system

ABSTRACT

The present invention relates to a susceptor system for an apparatus of the type adapted to treat substrates and/or wafers; the susceptor system is provided with a cavity ( 1 ) which acts as a chamber for the treatment of the substrates and/or wafers and which extends in a longitudinal direction and is delimited by an upper wall ( 2 ), by a lower wall ( 3 ), by a right-hand side wall ( 4 ), and by a left-hand side wall ( 5 ); the upper wall ( 2 ) is constituted by at least one piece of electrically conducting material suitable for being heated by electromagnetic induction; the lower wall ( 3 ) is constituted by at least one piece of electrically conducting material suitable for being heated by electromagnetic induction; the right-hand side wall ( 4 ) is constituted by at least one piece of inert, refractory and electrically insulating material; the left-hand side wall ( 5 ) is constituted by at least one piece of inert, refractory and electrically insulating material; the piece of the upper wall ( 2 ) is thus electrically well insulated from the piece of the lower wall ( 3 ).

The present invention relates to a susceptor system for an apparatus ofthe type adapted to treat substrates and/or wafers.

In order to produce integrated circuits, it is necessary to treatsubstrates and/or wafers; these may be made of a single material(semiconducting or insulating) or of several materials (conducting,semiconducting and insulating); the term “substrate” and the term“wafer” often refer in practice to the same thing, that is, a thinelement which is very often disc-shaped; the former term is usually usedwhen the element serves basically solely for supporting layers orstructures of semiconducting material; the second is usually used in allother cases.

There are purely thermal treatments and chemical/physical treatmentswhich involve heating.

In general, in order to grow semiconducting materials (Si, Ge, SiGe,GaAs, AlN, GaN, SiC, . . . ) epitaxially on substrates, hightemperatures are required if the quality of the material grown is to besuitable for microelectronic applications. For semiconducting materialssuch as silicon, temperatures typically of from 1000° C. to 1100° C. areused. For semiconducting materials such as silicon carbide, even highertemperatures are required; in particular, temperatures typically of from1500° C. to 2000° C. are used.

A reactor for the epitaxial growth of silicon carbide or similarmaterial therefore requires, amongst other things, a system whichgenerates heat so that these temperatures can be achieved inside areaction chamber, naturally it is desirable for the system to generateheat not only effectively but also efficiently. For these reasonsreaction chambers with hot walls are used in reactors of these types.

One of the most suitable methods of heating the walls of a reactionchamber is the method based on electromagnetic induction; an elementmade of conducting material, an inductor, and an alternating electricalcurrent (having a frequency typically of between 2 kHz and 20 kHz) areprovided, the electrical current is caused to flow in the inductor so asto generate a variable magnetic field, the element is positioned in amanner such that it is immersed in the variable magnetic field; theelectrical currents induced in the element because of the variablemagnetic field cause heating of the element by the Joule effect; aheating element of this type is known as a susceptor and can be useddirectly as a wall of the reaction chamber, if suitable materials areused.

A reactor for the epitaxial growth of silicon carbide or similarmaterial also requires the reaction chamber to be well insulatedthermally from the outside environment particularly to limit heatlosses, and to be well sealed to prevent, on the one hand, dispersal ofreaction gases contaminating the outside environment and, on the otherhand, entry of gases from the outside environment contaminating thereaction environment.

Some known susceptors suitable for use in reactors for the epitaxialgrowth of silicon carbide are described briefly below.

American patent U.S. Pat. No. 5,879,462 describes a cylindricalsusceptor (of circular cross-section) which has an internal cavity(which acts as a reaction chamber), extending in a longitudinaldirection and having a substantially rectangular cross-section; thissusceptor is made entirely of silicon carbide in powder form; heatingtakes place by means which radiate a radiofrequency field.

American patent U.S. Pat. No. 5,674,320 describes a cylindricalsusceptor (of substantially elliptical cross-section) which has twointernal cavities (which act as reaction chambers) extending in alongitudinal direction and having identical and substantiallyrectangular cross-sections; this susceptor can be formed as a singlepiece or in two identical pieces each of which has an internal cavity;the pieces of the susceptor are made of graphite and are coated with alayer of silicon carbide; in the two-piece susceptor, the pieces arejoined together mechanically by means of graphite screws and areelectrically insulated from one another, in particular by the layer ofsilicon carbide; heating takes place by electromagnetic induction: theelectrical currents induced in the graphite flow all around each cavity.

American patent U.S. Pat. No. 5,792,257 describes a cylindricalsusceptor (of substantially elliptical cross-section) which has aninternal cavity (which acts as a reaction chamber), extending in alongitudinal direction and having a substantially rectangularcross-section; the susceptor is made of graphite and is coated with alayer of silicon carbide; heating takes place by electromagneticinduction; the electrical currents induced in the graphite flow allaround the cavity; in order to protect the region of the cavity on whichthe substrate to be grown is supported, a small silicon carbide plate isprovided, fitted on the lower wall of the cavity, and the substrate isplaced thereon.

American patent U.S. Pat. No. 5,695,567 describes a prismatic susceptor(of hexagonal cross-section) which has an internal cavity (which acts asa reaction chamber), extending in a longitudinal direction and having arectangular cross-section; this susceptor is made in four pieces; thepieces of the susceptor are made of graphite and are coated with a layerof silicon carbide; the pieces are joined to one another mechanically bymeans of graphite screws; two silicon carbide plates cover the upper andlower pieces of the susceptor so as to separate the side pieces from theupper and lower pieces; heating takes place by electromagneticinduction; the electrical currents induced in the graphite flow withineach piece which delimits the cavity.

The object of the present invention is to provide a susceptor system foran apparatus of the type adapted to treat substrates and/or wafers,which is adapted to be heated by electromagnetic induction, which heatsthe treatment chamber uniformly, effectively and efficiently, which doesnot have electrical sparks problems, and which is also of simpleconstruction.

This object is achieved by the susceptor system having thecharacteristics set out in independent claim 1.

The concept upon which the present invention is based is that ofproviding a treatment chamber in the form of a cavity delimited by fourwalls, but of using only two of the four walls for actively heating thechamber and using the other two walls to heat the chamber passively andto keep the first two walls electrically insulated.

Advantageous characteristics of the susceptor system according to thepresent invention are set out in the claims that are directly orindirectly dependent on claim 1.

According to a further aspect, the present invention also relates to anapparatus for treating substrates and/or wafers, having thecharacteristics set out in independent claim 15.

Advantageous characteristics of the apparatus according to the presentinvention are set out in the claims that are directly or indirectlydependent on claim 15.

The present invention will become clearer from the following descriptionwhich is to be considered jointly with the appended drawings, in which:

FIG. 1 is a schematic, axonometric view of a susceptor system accordingto the present invention, with some additional elements,

FIG. 2 is a schematic view showing, in section, a detail of a susceptorsystem according to the present invention with some additional elements,

FIGS. 3 a and 3 b are schematic, axonometric views of the lower wall ofa susceptor system according to the present invention provided with aslide, with the slide fully inserted and with the slide removed,respectively,

FIG. 4 is a detailed view, partially in section, of the lower wall of asusceptor system according to the present invention with a slide and arotatable disc, and

FIG. 5 is a partial detailed top view, of the slide of the wall of FIG.4, without the disc.

The present invention will be described below with reference to theembodiments shown in FIGS. 1, 2 and 3, but is not limited to theseembodiments.

The susceptor system according to the present invention is designedspecifically for an apparatus of the type adapted to treat substratesand/or wafers; it is provided with a cavity, indicated 1 in thedrawings, which acts as a chamber for the treatment of the substratesand/or wafers and which extends in a longitudinal direction.

The cavity is delimited by an upper wall, indicated 2 in the drawings,by a lower wall, indicated 3 in the drawings, by a right-hand side wall,indicated 4 in the drawings, and by a left-hand side wall, indicated 5in the drawings.

The upper wall 2 is constituted by at least one piece of electricallyconducting material which is suitable for being heated byelectromagnetic induction; the lower wall 3 is constituted by at leastone piece of electrically conducting material which is suitable forbeing heated by electromagnetic induction; the right-hand side wall 4 isconstituted by at least one piece of inert, refractory and electricallyinsulating material; the left-hand side wall 5 is constituted by atleast one piece of inert, refractory and electrically insulatingmaterial. The upper wall 2 is therefore electrically insulated from thelower wall 3.

In the embodiment of FIG. 1, the susceptor system is constituted purelyand simply by the four pieces constituted by the four walls 2, 3, 4, 5.In the embodiment shown partially in FIG. 2, a further two elements areincluded in the susceptor system, but the pieces comprising the fourwalls nevertheless constitute its core.

The treatment chamber in the form of a cavity is thus delimited by thefour walls of the susceptor system; two of these walls (the upper wall 2and the lower wall 3) heat the chamber actively, whereas the other two(the side walls 4 and 5) heat the chamber passively; moreover,electrical sparks could occur solely directly between the upper wall 2and the lower wall 3 and this is improbable because of the distance;finally, the currents induced in the upper wall 2 and in the lower wall3 are independent of one another.

In the embodiments shown in the drawings, each of the walls 2, 3, 4, 5is constituted by a single piece; this is advantageous from theconstructional point of view.

A substance which is particularly suitable for producing the pieces madeof conducting material for the wall 2 and the wall 3 is graphite;however, graphite cannot withstand the typical environment of atreatment chamber and therefore has to be coated with a layer ofmaterial that is more resistant from the chemical and thermal points ofview.

A compound suitable for producing the coating layer is silicon carbide;however, if the chamber is also used for the epitaxial growth of siliconcarbide, it is preferable to use even more resistant compounds such asniobium carbide, boron carbide, or tantalum carbide; amongst otherthings, the latter two also have the advantage of being electricalconductors.

Other compounds usable to produce the coating layer are some nitrides;amongst these, silicon nitride, aluminium nitride and, in particular,boron nitride may be mentioned. Nitrides are to be used with great careif, for example, silicon carbide is to be treated in the chamber, infact, if nitrogen atoms should become detached from the coating layer,they would dope the silicon carbide.

Naturally, the coating of the graphite is strictly necessary only in theareas of the pieces that are adjacent to the cavity 1, but it maysometimes be more convenient to produce complete coatings, or at leastbeyond the necessary minimum.

It should be explained that the above-mentioned chemical substances havephysical properties which depend on their allotropic form and also onthe production process; for example, carbon, silicon carbide, and boronnitride have more than one stable allotropic form, with quite differentphysical properties; again, for example, with graphite it is possible toproduce materials with good thermal and electrical conductivity andmaterials with poor thermal and electrical conductivity; finally, theaddition of chemical compounds to a material can modify some of itsphysical properties.

The coating layer may be produced basically in two ways: by chemicalreaction, or by physical application. For example, a layer made of acarbide can generally be produced more easily by chemical reaction on agraphite piece. There are companies that are specialized in producingsuch layers.

As far as the thickness of the coating layer is concerned, for siliconcarbide, it may be, for example, 100 m and for tantalum carbide, forexample 20 m; the thickness to be used may depend, amongst other things,on the properties of the material and on the function required.

A compound which is particularly suitable for the production of piecesmade of inert, refractory and electrically insulating material for theside walls 4 and 5 is silicon carbide; in this case, moreover, thepieces conduct heat well and thus achieve good passive heating.

Another compound which is particularly suitable for producing the piecesmade of inert, refractory and electrically insulating material for theside walls 4 and 5 is boron nitride; in this case also, the piecesconduct heat well and thus achieve good passive heating; in fact thiscompound has a hexagonal allotropic form with physical propertiessimilar to those of graphite and a cubic allotropic form with physicalproperties similar to those of diamond; one or other allotropic form canbe produced, according to the production process.

The external shape of the cross-section of the susceptor systemaccording to the present invention is advantageously substantiallyuniform in the longitudinal direction and substantially circular orsubstantially elliptical; the susceptor system is in fact thus easy toproduce and can easily be coupled well with an inductor for heating it.

The shape of the cross-section of the cavity, that is, of the treatmentchamber, is also advantageously substantially uniform in thelongitudinal direction; the susceptor system is in fact thus easy toproduce.

In known reactors, the cross-section of the chamber reduces in thelongitudinal direction to compensate for the reduced concentration ofthe precursors. Instead, the present invention solves this problem bycausing the substrates or wafers to rotate and using a high flow ofreaction gas; this high gas-flow also has the advantage of effectivelyand quickly removing any solid particles from the reaction chamber.

The average width of the cavity 1, that is, of the treatment chamber, ispreferably at least three times, even more preferably at least fivetimes, the average height of the cavity 1; the heating of the treatmentchamber is in fact thus due to a greater extent to the walls 2 and 3,that is, to the walls which heat the chamber actively.

The pieces for the side walls may simply have a cross-section having asubstantially rectangular or trapezoidal shape; this is the case in theembodiments of FIG. 1 and of FIG. 2.

According to a particularly effective solution, the piece for the upperwall 2 and/or the piece for the lower wall 3 have cross-sections havingthe external shape substantially of a segment of a circle or of asegment of an ellipse; this is the case in the embodiments of FIG. 1 andFIG. 2; the area traversed by the magnetic field of the inductor is infact thus large and the currents induced are therefore large.

The pieces for the four walls 2, 3, 4, 5 may simply be placed closetogether and inserted in a suitable compartment; this is the case in theembodiment of FIG. 1. Advantageously, the piece for the upper wall 2and/or the piece for the lower wall 3 have grooves and/or ribs in thelongitudinal direction for joining with the pieces for the side walls 4,5; the structure of the susceptor system is thus firmer, even though itscomponent parts are no more difficult to produce; this is the case inthe embodiment of FIG. 2, in which the wall 2 has two lateral grooves 22(of which only one is shown in the drawing) and the wall 3 has twolateral grooves 32 (of which only one is shown in the drawing).

In all of the embodiments shown in the drawings, the piece for the upperwall and/or the piece for the lower wall are hollow; the mass of thesusceptor system is thus very low and it can therefore be heated (andalso cooled) very quickly.

If the piece is hollow so as to have a large through-hole which extendsin the longitudinal direction, the currents induced in the wall arenecessarily confined to its peripheral region and thus flow very closeto the treatment chamber, in which they generate heat. The number ofthrough-holes for each wall may in fact be greater than one, but theeffect does not change substantially.

In the embodiments of FIG. 1 and of FIG. 2, each of the upper wall 2 andthe lower wall 3 has a single through-hole, indicated 21 or 31,respectively.

The embodiment shown partially in FIG. 3 has various advantageouscharacteristics which will be described below.

The susceptor system according to the present invention mayadvantageously comprise a slide, indicated 6 in FIG. 3, mounted withinthe cavity 1, that is, in the treatment chamber, and suitable forsupporting at least one substrate or at least one wafer; the slide 6 canslide in guided manner in the longitudinal direction; operations toinsert and remove substrates or wafers are thus facilitated; in fact thesubstrates or wafers are manipulated outside the treatment chamber andare inserted and removed by the movement of the slide.

In practice, it is convenient to arrange for the lower wall, indicated 3in FIG. 3, to have a guide, indicated 33 in FIG. 3, which is suitablefor receiving the slide, indicated 6 in FIG. 3, and which extends in thelongitudinal direction in a manner such that the slide can slide alongthe guide. In the embodiment of FIG. 3, the guide is formed entirelywithin the wall 3 and the slide 6 has a flat upper surface that issubstantially aligned with the flat upper surface of the wall; theeffective cross-section of the treatment chamber is thus substantiallyrectangular and regular (as if the slide were not provided).

To achieve a more uniform treatment of the substrates or wafers, theslide may comprise at least one disc suitable for supporting at leastone substrate or at least one wafer and may be provided with a recessfor housing the disc rotatably, in the embodiment of FIG. 3, the slide 6is provided with a recess 62 and comprises a single disc 61.

With regard to the materials of the disc and of the slide, theembodiment of FIG. 3 is made in the manner described below.

The slide 6 is made of graphite coated with a layer of tantalum carbide;the slide 6 thus also acts as a susceptor since it is immersed in themagnetic field and it is an electrical conductor, moreover, the currentsinduced in the wall 3 can also flow in the slide 6 since the tantalumcarbide layer is an electrical conductor and does not therefore insulatethe slide 6 electrically from the wall 3.

The disc 61 is made of graphite coated with a layer of tantalum carbide;the disc 61 thus also acts as a susceptor since it is immersed in themagnetic field and is an electrical conductor; the currents induced inthe wall 3 and in the slide 6 cannot, however, flow in the disc 61because, when the disc 61 rotates, it is kept slightly raised from theslide (whilst remaining substantially within its recess 62), by agas-flow.

In apparatus for the treatment of substrates and/or wafers and, inparticular, in epitaxial reactors, it is quite common to rotate thesupport for the substrates; this rotation is generally performed bymeans of a motor which is disposed outside the treatment chamber andwhich imparts a rotary motion to the support via suitable transmissionmeans.

This method of rotation functions well but has the disadvantage ofrequiring either transmission means which can withstand the environmentof the treatment chamber, or sealing means which enable a rotary motionto be transmitted, or both; these requirements are even more difficultto satisfy in reactors for the growth of materials such as siliconcarbide because of the very high temperatures; moreover, in a susceptorwith a slide such as that shown in FIG. 3, the drive-transmission meanswould have to be opened when the slide were removed and closed when theslide were inserted, which is very complex to achieve.

To solve this problem, it has been planned to use a different method ofrotation based on the use of a gas-flow.

The solution adopted is described below with the aid of FIG. 4 and FIG.5, with non-limiting reference to an epitaxial reactor.

A support 610 is provided for a predetermined number (for example one,three, four, five, . . . ) of substrates; the support 610 hassubstantially the shape of a thin disc and has, on its upper side,recesses (not shown in the drawings) for housing the substrates and, onits lower side, a central cylindrical pin 611 which projects from asmall cylindrical recess 612; the pin 611 serves to hold the support 610in position and to guide its rotation; moreover, the two faces of thesupport 610 are flat.

A slide 600 is also provided for housing the support 610; the slide 600has substantially the shape of a thick rectangular plate; on its upperside, the slide 600 has a large cylindrical recess 601 for the completeinsertion of the support 610, from which recess a small central cylinder602 projects, with a blind hole 603 for the complete insertion of thepin 611 of the support 610; in the base of the large recess 601 there isa first shallow, centred, cylindrical recess 604 with a diameter whichis much smaller, for example, by half; in the base of the large recess601, there is a predetermined number of very shallow, straight channels605 (in FIG. 5 there are four channels, but there could also be three orfive, six, seven, eight, . . . channels) which start from the firstshallow recess 604 and extend tangentially therefrom; also in the baseof the large recess 601, in the vicinity of its perimeter, there is adeep circular groove 606; an outlet duct (not shown in the figures) isalso formed inside the slide 600, starting from the groove 606; on itslower side, the slide 600 has a second shallow cylindrical recess 607,which is centred relative to the first shallow recess 604 and is incommunication therewith by means of a predetermined number (in FIG. 5,there are two, but there could also be one or three, four, . . . ) ofshort, oblique, cylindrical ducts 608 (which, alternatively, could bevertical).

Finally, one wall 300 of the susceptor system has a guide (not shown inthe drawings) for housing the slide 600; the slide 600 can slide alongthe guide but remains stationary during epitaxial growth processes; thewall 300 also has a long duct 301 which opens in the base of the guidein a vertical direction, in the region of the second shallow recess 607of the slide 600 (in FIG. 4, the duct 301 opens in a centred positionbut it could also open in an eccentric position relative to the axis ofsymmetry of the support 610).

The method adopted is summarized in the following paragraph.

A flow of gas is caused to enter the wall duct 301 that opens in thebase of the slide guide; the gas-flow enters the recess 607 of theslide, passes to the recess 604 of the slide through the ducts 608 ofthe slide and creates, in the recess 604 of the slide, a pressure whichlifts the support 610 slightly, the gas under pressure in the recess 604of the slide is urged into the channels 605 of the slide and collects inthe groove 606 of the slide; the flow of the gas along the channels 605of the slide brings about rotation of the slightly raised support 610,by friction.

A susceptor system of this type is typically usable in an apparatus ofthe type adapted to treat substrates and/or wafers; this is a furtheraspect of the present invention.

The apparatus according to the present invention will be described belowwith non-limiting reference to FIG. 1 and FIG. 2.

The apparatus according to the present invention comprises, essentially,a susceptor system provided with a cavity which acts as a treatmentchamber, extends in a longitudinal direction, and is delimited by aconducting upper wall, by a conducting lower wall, by an insulatingright-hand side wall and by an insulating left-hand side wall.

The apparatus according to the present invention may also advantageouslycomprise a first refractory and thermally insulating structure 7 that issuitable for surrounding the susceptor system (formed in FIG. 1 by thefour walls 2, 3, 4, 5) and is constituted, essentially, by a tube ofhigh-porosity graphite or of similar refractory and thermally insulatingmaterial, which extends in the longitudinal direction.

Known refractory and thermally insulating structures for theseapparatuses are formed as single pieces.

At the experimental stage of the present invention, it was planned toproduce a structure of this type by means of two or more pieces ofhigh-porosity graphite, which would be very convenient from theconstructional point of view, and to place graphite having a softfelt-type structure between the pieces so as to achieve a good jointbetween the various pieces and to maintain the thermal insulation.

If one of these known structures is made of a material which is at leastslightly conducting (such as high-porosity graphite) and if it is usedin an apparatus heated by electromagnetic induction, electrical currentsmay be established within the structure; these currents may be due inpart to the electromagnetic induction within the structure and in partto contact with the susceptor; if some of the current induced in thesusceptor is dispersed elsewhere, the efficacy and the efficiency of thesusceptor is therefore reduced.

To solve this problem, it was planned to made a structure of this typeby means of two or pieces of high-porosity graphite or of similarconducting material, which would be very convenient from theconstructional point of view, and to place elements of refractory,thermally insulating and electrically insulating material between thepieces; for example, silicon carbide, or boron nitride, preferablyporous, may be used for this material.

In the embodiment of FIG. 2, the graphite tube is divided, in thelongitudinal direction, into two half-tubes 71 and 72; the structure 7comprises, in addition to the two half-tubes 71 and 72, two elements 73(of which only one is shown in the drawing) of refractory, thermallyinsulating and electrically insulating material, which extend in thelongitudinal direction and which are disposed between the two half-tubes71 and 72.

The apparatus according to the present invention may also advantageouslycomprise a second, hermetic structure 8 suitable for surrounding thefirst structure 7; this facilitates the choice of materials.

The hermetic structure may be constituted substantially by a tube ofquartz or similar material which surrounds the refractory structure,extends in the longitudinal direction, and has a substantially uniformand substantially circular or substantially elliptical externalcross-sectional shape; this is the case in the embodiment of FIG. 1.

Alternatively, the hermetic structure may be constituted substantiallyby a tube of quartz or similar material which surrounds the refractorystructure and which extends in the longitudinal direction, and by ametal tube which surrounds the quartz tube; in this case, the externalshape of the cross-section of the quartz tube is not very importantsince mechanical stresses are withstood by the metal tube.

The apparatus according to the present invention may also advantageouslycomprise electrical conduction means 9 which are suitable for heatingthe susceptor system by electromagnetic induction and which are woundaround the first structure 7 or the second structure 8; this is the casein the embodiment of FIG. 1.

If the susceptor system of the apparatus has walls provided withthrough-holes, as in the embodiments shown in the drawings, theapparatus may advantageously comprise means suitable for causing atleast one gas-flow to flow within at least one of the holes; thegas-flow may serve to remove any particles which are detached from theinternal walls of the hole; the gas-flow may also serve to modify thetemperature of the susceptor system slightly, argon or, more generally,an inert gas, is suitable in particular for the former function;hydrogen, for example, is suitable in particular for the latter functionand, more particularly, for cooling.

The apparatus according to the present invention can be used, with theaddition of further components, as a reactor for the epitaxial growth ofsilicon carbide or similar material on substrates.

Silicon carbide is a semiconducting material which is very promising butalso very difficult to handle; most of the characteristics set out aboveare designed particularly for this use and for this material.

The apparatus according to the present invention may also be used, withthe addition of further components, as apparatus for thehigh-temperature thermal treatment of wafers.

1. A susceptor system for an apparatus of the type adapted to treatsubstrates and/or wafers, the susceptor system being provided with acavity (1) which acts as a chamber for the treatment of the substratesand/or wafers and which extends in a longitudinal direction and isdelimited by an upper wall (2), by a lower wall (3), by a right-handside wall (4), and by a left-hand side wall (5), the upper wall (2)being constituted by at least one piece of electrically conductingmaterial suitable for being heated by electromagnetic induction, thelower wall (3) being constituted by at least one piece of electricallyconducting material suitable for being heated by electromagneticinduction, the right-hand side wall (4) being constituted by at leastone piece of inert, refractory and electrically insulating material, theleft-hand side wall (5) being constituted by at least one piece ofinert, refractory and electrically insulating material, so that the oreach piece of the upper wall (2) is electrically insulated from the oreach piece of the lower wall (3), the pieces (2, 3, 4, 5) being includedin the susceptor system.
 2. A susceptor system according to claim 1 inwhich each of the walls (2, 3, 4, 5) is constituted by a single piece.3. A susceptor system according to claim 1 in which the or each piece ofthe upper wall (2) and of the lower wall (3) is made of graphite orsimilar electrically conducting material and is coated with a layer ofsilicon, tantalum, niobium, or boron carbide, or of silicon, boron, oraluminium nitride, or of similar inert and refractory material, at leastin the areas adjacent the cavity (1).
 4. A susceptor system according toclaim 1 in which the or each piece of the side walls (4, 5) is made ofsilicon carbide or of boron nitride.
 5. A susceptor system according toclaim 1 in which the external shape of the cross-section of thesusceptor system is substantially uniform in the longitudinal directionand is substantially circular or elliptical.
 6. A susceptor systemaccording to claim 1 in which the shape of the cross-section of thecavity (1) is substantially uniform in the longitudinal direction.
 7. Asusceptor system according to claim 1 in which the average width of thecavity (1) is at least three times, more preferably at least five times,the average height of the cavity (1).
 8. A susceptor system according toclaim 1 in which the pieces of the side walls (4, 5) have cross-sectionsof substantially rectangular or trapezoidal shape.
 9. A susceptor systemaccording to claim 1 in which the piece of the upper wall (2) and/or thepiece of the lower wall (3) have cross-sections having the externalshape substantially of a segment of a circle or a segment of an ellipse.10. A susceptor system according to claim 1 in which the piece of theupper wall (2) and/or the piece of the lower wall (3) have grooves (22,32) and/or ribs in the longitudinal direction for joining with thepieces of the side walls (4, 5).
 11. A susceptor system according toclaim 1 in which the piece of the upper wall (2) and/or the piece of thelower wall (3) is hollow so as to have at least one hole (21, 31),preferably a through-hole, which extends in the longitudinal direction.12. A susceptor system according to claim 1 comprising a slide (6)mounted inside the cavity (1) and suitable for supporting at least onesubstrate or at least one wafer, the slide (6) being slidable in guidedmanner in the longitudinal direction.
 13. A susceptor system accordingto claim 12 in which the lower wall (3) has a guide (33) which issuitable for receiving the slide (6) and which extends in thelongitudinal direction so that the slide (6) can slide along the guide(33).
 14. A susceptor system according to claim 12 in which the slide(6) comprises at least one disc (61) suitable for supporting at leastone substrate or at least one wafer, and is provided with a recess (62)suitable for housing the disc (61) rotatably.
 15. Apparatus of the typeadapted to treat substrates and/or wafers, characterized in that itcomprises at least one susceptor system (2, 3, 4, 5) according toclaim
 1. 16. Apparatus according to claim 15, comprising a firstrefractory and thermally insulating structure (7) which surrounds thesusceptor system (2, 3, 4, 5) and is constituted substantially by a tubeof high-porosity graphite or similar material and which extends in thelongitudinal direction.
 17. Apparatus according to claim 16 in which thetube is divided, in the longitudinal direction, into two half-tubes (71,72) and the first structure (7) further comprises two elements (73) ofrefractory, thermally insulating and preferably electrically insulatingmaterial which extend in the longitudinal direction and are disposedbetween the two half-tubes (71, 72).
 18. Apparatus according to claim 15comprising a second, hermetic structure (8) suitable for surrounding thefirst structure (7).
 19. Apparatus according to claim 15 comprisingelectrical conduction means (9) which are suitable for heating thesusceptor system by electromagnetic induction and which are wound aroundthe first structure (7) or around the second structure (8). 20.Apparatus according to claims 15 to 19, comprising means for causing atleast one gas-flow to flow in at least one through-hole (21, 31) of thesusceptor system.
 21. Apparatus according to any one of claim 15characterized in that it is a reactor for the epitaxial growth ofsilicon carbide or similar material on substrates.
 22. Apparatusaccording to claim 15 characterized in that it is an apparatus for thehigh-temperature thermal treatment of wafers.